Automatically variable pitch propeller



Jan. 9, 1934. 5 DE LAVAUD 1,943,210

AUTOMATICALLY VARIABLE PITCH PROPELLER Filed Nov. 14, 1931 s Sheets-Sheet 1 lure/viva Jan. 9, 1934. D. 5. DE LAVAUD 1,943,210

AUTOMATICALLY VARIABLE PITCH PROPELLER Filed Nov. 14, 1951 6 Sheets-Sheet 2 Jan. 9, 1934. D. 5. DE LAVAUD 1,943,210

A AUTOMATICALLY VARIABLE PITCH PROPELLER 6 ShTets-Sheet 3 Filed Nov. 14, 1951 72561440 J6 Zrauf/ Jan. 9, 1934. D. s. DE LAVAUD 1,943,210

AUTOMATICALLY VARIABLE PITCH PROPELLER Filed Nov. 14, 1931 6 Sheets-Sheet 4 M re/V7 13 Jan. 9, 1934. D. 5. DE LAVAUD 1,943,210

AUTOMATICALLY VARIABLE PITCH PROPELLER Filed Nov. 14, 1931 e Sheets-Sheet 5 A v /um R mzdw Jan. 9, 1934. D. s. DE LAVAUD AUTOMATICALLY VARIABLE PITCH PROPELLER 6 Sheets-Sheet '6 Filed Nov. 14, 1931 will Patented Jan. 9, 1934 UNITED STATES AUTOMATICALLY VARIABLE PITCH PROPELLER Dimitri Sensaud de Lavaud, Paris, France Application November 14,

1931, Serial No. 575,431,

and in France November 14, 1930 10 Claims.

This invention has for object an airplane propeller the pitch of which is automatically variable during flight.

Propellers already exist in which the blades are freely pivoted in the hub, and in which an aerodynamic torque tending to reduce the pitch is balanced by an antagonistic centrifugal torque, this result being obtained by giving to the blade a yataghan shape, or by inclining its neutral axis on the pivoting axis.

These propellers in which use is necessarily made of a centrifugal torque depending on the pivotal movement do not give any pure centrifugal regulation and do not allow of determining at will the position of equilibrium.

The propeller according to the invention essentially differentiates from propellers already known in that the centrifugal torque, which is exerted on the blade in the direction of the increasing pitches, is rendered practically independent of the pivotal movement, that is to say of the incidence of the blade, or even varies in the same direction as this incidence, and in that balance is obtained between three torques: an aerodynamic torque tending to reduce the pitch, the above mentioned centrifugal torque, which is preferably always greater than the aerodynamic torque, and a resilient torque depending only on the pivotal movement of the blade.

In order to render the centrifugal torque practically independent of the pivotal movement, the neutral axis of the blade is arranged, according to an important feature of the invention, in such a manner that it does not pass through the axis of rotation of the propeller, so as to use, for producing the centrifugal torque, no longer the leverage determined by the displacement in the direction of advance of the centre of gravity, displacement which is variable according to the pivotal movement, but, on the contrary, the leverage, due to the displacement of the neutral axis in the direction of rotation, displacement which 'is practically constant in the limits of the pivotal movement of the blade.

In the initial position of the propeller, the neutral axis is preferably placed in a plane perpendicular to the axis of rotation, so that, in this position, there is no displacement in the direction of advance and that the torque due to such a displacement is null; and with each blade is combined a centrifugal compensating device so arranged as to be in unstable equilibrium in the normal position, in order that the influence of this compensating device annuls that of the displacement of the centre of gravity in the direction of advance, when the blade pivots. fiuence of the torque due to this unavoidable displacement is therefore eliminated, and it is obvious that it is possible to obtain, by means of the/compensating device, a torque greater The in than and of reverse direction to the preceding one, for increasing at will the accuracy and amplitude of the regulation.

Consequently, the invention consists in obtain ing at every instant the equilibrium of the pivotalmovement of three torques:

(a) An aerodynamic torque tending to reduce the pitch;

(b)A resultant centrifugal torque regulated by a compensating device, tending to increase the pitch, preferably greater than the aerodynamic torque, independent of the pivotal movement or even varying in the same direction as the pitch; a portion of this torque must obviously balance the natural torsion torque of the blade about its neutral axis and which tends to reduce the pitch;

(c)A resilient torque completing the balance of the pivotal movement and preferably tending, consequently, to reduce'the pitch.

Another feature of the invention consists in obtaining the resilient torque by means of a torsion rod laterally arranged relatively to the nose of the engine, therefore of great length, and at the same time maintaining the blade against the action of centrifugal force, this blade being moreover held by a guide tube mounted on ball bearings. In this way the necessity of absorbing the centrifugal force on ball bearings is avoided, this being the cause of irregularity in the operation.

The invention is clearly illustrated in the accompanying drawings, in which:-

Figure 1 shows a projection on a vertical plane at right angles to the axis of rotation of the propeller.

Figure 2 shows the projection on a horizontal plane.

Figure 3 shows the projection on a lateral plane.

Figure 4 is an elevation, the nose of the engine being placed in front of the plane of figure.

Figure 5 is a sectional side View relating to Fig. 4, and made according to line VV of Fig. 4.

Figure 6 is a sectional plan view relating to Fig. 5, and made according to line VI-VI of this figure.

Figures '7 and 8 are respectively an end view and a side view of a propeller according to the invention.

Figure 9 is a plan view thereof.

Figure 10 is a diagrammatic view, 1

Figure 11 is a sectional side view of a propeller according to the invention applied to an engine provided with a compressor,

Figure 12 is a corresponding front view thereof, Figure 13 is a partial sectional side view of the propeller shown in Fig. 11, and

- Figures 14, 15 and 16 are cross sections of constructional modifications of the torsional rods.

In Qrder to fully explain the principle of operation of the propeller according to the invention, Figs. 1, 2 and 3 of the accompanying drawings diagrammatically illustrate a propeller in which, for general purposes, the neutral axis has 5 been inclined in the direction of advance, (as is known), and has been caused to pass outside the axis of rotation of the propeller (according to the essential feature of the invention).

On a plane perpendicular to the axis 0 of rotation, the neutral fibre of a blade, which in this example is assumed to be rectilinear, is projected according to a straight line A B (Fig. 1) situated relatively to the axis 0 with a displacement e in the direction 1 of the rotation. This displacement allows, in its initialposition, the total compensation of the blade by a centrifugal torque relatively to the torques due to the resistance to rotation and to the propelling stress.

The blade pivots on a torsion rod A D displaced relatively to the axis 0 in a direction reverse to the rotation.

This rod A D supports the centrifugal pull and, being laterally located relatively to the nose of the engine, can have a sufiicient length for ensuring, in torsion, the distortions necessary for the automaticity.

The lateral reactions are absorbed by a guide tube coaxial with the torsion rod, rotating on ball bearings and capable of resisting, by abutting, to the centrifugal pull as soon as the torsion rod has lengthened to a given amount.

The tension stress of the central rod is'thus automatically limited in case the speed of rotation should become excessive.

Owing to such an assemblage:

(a) The propelling stress, parallel to the axis of rotation, applied at the centre of pressure I of the blade, acts, upon pivoting, with the leverage h, distance from I to the torsion rod.

As the leverage it may be considerable, the sensitiveness or accuracy of the regulation, rela tively to the variation of the propelling stress, is always suflicient.

(b) The centrifugal stress G H, exerted on the blade at its centre of gravity, is directed according to the perpendicular dropped from this point on the axis of rotation.

In the general example illustrated, it has two components, one N parallel to the vertical projection of the torsion rod, the other T perpendicular.

T supplies a centrifugal torque C tending to increase the pitch as soon as the rectilinear neutral axis of the blade is inclined forwardly, so that the horizontal projection of the centre of gravity G comes in front of the horizontal projection of A, according to a quantity reckoned parallel to the axis 0. If the neutral axis was rearwardly inclined, the torque C generated by T, would tend to diminish the pitch.

In a plane passing through the torsion rod and parallel to the axis of rotation, this rod is forwardly inclined, this having a double result:

(a) The centrifugal component N becomes oblique relatively to the rod, its component perpendicular to this rod tending to increase the pitch and producing a second regulating centrifugal torque C (b) The resistance to rotation of the blade, passing behind the torsion rod, tends, as the propelling stress, to reduce the pitch.

The justifying calculation of the torques C and C is very simple.

It will first be assumed that the torsion rod is perpendicular to the axis of rotation. The celltrifugal resultant H intersects at A the plane drawn through the point A of the torsion rod at right angles to this rod. The point A is in front of the plane of figure according to a quantity 6 measuring the forward displacement of the centre of gravity of the blade. The stress H is decomposed into N and T, the first laterally displaced to the extent of a and forwardly displaced to the extent of a. The single driving torque tending to increase the pitch is T6, whilst the two compensating torques of the blade are N6 and N6. It is easy to see that, for all the sections, the compensation is maintained in a sufficiently accurate mamier. bearings is T.

It will now be assumed that the point A where the neutral axis meets the torsion rod remaining fixed; the torsion rod is forwardly inclined according to the angle 5', the point D passing behind the plane of figure. l

The moment, relatively to the point A of T is T6 and its projection on the axis of the rod is the centrifugal torque Q =T6 cos But if 5 is the inclination of N on G H, then T=N tg so that C =N6 sin cos cos q) Concerning the second centrifugal torque, N is projected on a plane perpendicular to the rod according to the force N sin 11 producing, about the rod, the second centrifugal torque C =N6 sin tending to increase the pitch.

It will be seen that there is complete analogy between both torques C and C the centrifugal L stress T being, for the first torque, associated with the variable leverage B and, for the second,-

the centrifugal stress N being associated with the constant leverage 6'.

When the blade pivots, the leverage 6 is subjected only to infinitely small variations, whilst the leverage 8 varies as the displacement of the centre of gravity of the blade.

In these conditions, for producing according to the invention a constant centrifugal torque,

use is made, no longer as has been done up to now, of the centrifugal component T associated with the variable leverage 6, but, on the contrary, the perpendicular component N associated with the leverage 6' which is practically constant. For that purpose, in the initial position; the

forward inclination of the neutral axis is first.

of all preferably avoided, in order to maintain only the displacement inthe direction of rotation, displacement which, associated with the forward inclination of the pivoting axis, is characteristic of the invention. The leverage 6 may be made sufiiciently great, in order to ensure, in horizontal flight near the ground, the total balancing of the blade relatively tolthe resistance function is to compensate the variations of this torque which would limit the amplitude and accuracy of the automatic regulation. The com- The lateral stress on the ball pensating device therefore always tends, in these conditions, contrarily to the torque C to accentuate a pivotal movement which has begun.

A supplementary centrifugal torque very rapid ly variable, is therefore introduced, and such that when the blade is caused to pivot in order to assume increasing pitches, it tends to, so much the more, increase the pitch as the pivotal movement is greater. On the contrary, when the blade is caused to pivot in order to assume decreasing pitches, it must tend to diminish the pitch, so much the more as the pivotal movement is greater.

It is thus possible, not only to compensate the variations of the centrifugal torque C, but by accentuating at will the action of the compensating device, to produce a real reinforcement of the regulation by the auxiliary action of this supplementary torque. In all cases, the accuracy and amplitude of the-regulation are controllable at will.

I For obtaining this result, use is made, for each blade, of a counterweight such that, under centrifugal action, it is in unstable position. Being pivoted on the hub, ,this counterweight transmits its action to the blade through a link so arranged that aslight pivoting movement of the blade produces large displacements of the counterweight and great variations of the torque it produces. It will thus be seen that such a counterweight, being in unstable positionunder centrifugal action, always tends to reinforce the pivoting movements of the blade and produces a supplementary torque satisfying the above mentioned conditions.

By varying the bulk, the leverage or the mounting of the counterweight, a .very precise adjustment of 'the regulation of 'the pitch is provided, allowing to obtain the desired number of revolutions with the greatest accuracy.

It will thus be seen that the operation of a propeller according to the invention allows to obtain:

(1) An aerodynamic regulation, that is to say a regulation relatively to the variations of the propelling stress and of the driving torque.

(2) A'centrifugal regulation, since one of the torques in presence does not depend on the speed.

(3) An adjustment as precise asdesired, through the compensating device, of the accuracy and amplitude of each of the, two regulations. '1

- Finally, the device has the advantage of automatically maintaining the compensation of the blades when the propelling stress increases. The pivoting for obtaining decreasing pitches which accompanies the increase of this propelling stress, forwardly displacing the centre of gravity of the blades, produces a compensating centrifugal torque which automatically balances the supplementary bending torque due to the propelling It is therefore possible to associate with stress. this device thin blades which are those having the bst'efliciency.

Use can even be made of extra thin blades,

pelling stress increases and the consecutive forward displacement ofthe centre of gravity would create a centrifugal torque C tending to increase the pitch and exactly balancing the variation of the aerodynamic torque. In order that starting may take place, thin blades must be used, but these blades must be distortable solely on a portion of their length, their rigidity being maintained near the place where the blade is inserted in the hub. The initial bending of the tip of the blade as soon as the propelling stress increases, does not prevent starting, as when the blade is caused to pivot, its resilient portion automatically straightens.

It is obvious that the invention includes in its scope:

1) The case in which the neutral axis of the blade is. arranged as described, but is not rectilinear. It can be slightly curved, askew, or plane, so as to obtain, section by section, the rigorous compensation of the blade.

(2), Any other device for causing the blades to pivot or for obtaining the resilient torque.

For instance, the blades may be caused to pivot on ball hearings or small pillars having spherical ends and simple or multiple springs can be added, these springs acting separately on each blade or on a common connecting member.

(3) Any other device for obtaining a resultant centrifugal torque, tending to increase the pitch, independent of the pivoting or varying in the same direction as the pitch, andfcombined with an aerodynamic torque and a resilient torque.

(4) The separate utilization of one of the devices forming the subject-matter of the patent or of several of them, as well as their modifications. Thus:

(a) The device for compensating the torque can be dispensed .with in case an average accuracy of regulation is desired.

(b) The leverage 6' can .be reversed by causing the pont A of Fig. l, to pass in front relatively to the direction of rotation. It is then necessary to rearwardly incline the torsion rods for again obtaining the centrifugal torque C tending to increase the pitch.

(5) The utilization of the characteristic arrangement of the blades or of the compensating device in the case of a propeller having a variable controllable pitch. The obtainment of the centrifugal torque C or of the compensating torque, has then for object to compensate the natural torsion tending to lock the blades at the minimum pitch and to thus allow a control as flexible as desired in both directions.

(6) The utilization of the compensating device on propellers for which the centrifugal torque used is the torque C for the purpose of controlling the balancing position.

By using the arrangements according to the invention, it is finally possible to obtain, during flight, an automatic rotation of the blades on themselves as soon as the engine tends to be driven by the propeller, which is then the receiver.

The engine sets and the pitch of the blades increases sufliciently in order that their aerodynamicjresistance 'may become negligible. This constitutes a considerable advantage on'multiengine airplanes, the qualities of flight of which, with a number of engines stopped, are considerably. improved.

The engines in action, owing to the regulation a considerable axial resistance, set and withdraw,

this materially reducing the resistance.

The double benefit obtained for the engines at rest and those in action is considerable.

For that purpose:

(a) Each blade is so arranged that the resultant aerodynamic torque of the propelling stress and of the resistance to rotation, overcomes the resultant centrifugal torque at the altitude at which the blades are be turned, so that the central rod is then twisted towards the decreasing pitches. This being provided in order that it should be possible, at this altitude, to re-start the stopped engines, their propellers immediately re-assuming their normal positions.

(b The torque compensating device is 50 mounted that it allows the blade to pivot in the direction of increasing pitches from a certain pivotal movement by a releasing device or a looking device.

(0) The torsion rod, at its end opposite to the blade, is free to rotate in the direction of increasing pitches, on a ball bearing combined with a resilient or like washer.

It is advantageous that, during normal running, the balls should not support the totality of the centrifugal pull and that a unilateral freedom should not be given to the rod, as, at a high altitude, the aerodynamic torque is always inferior to the centrifugal torque.

This result is obtained by arranging the ball raceway on a resilient abutment plate, so that, during normal running, this plate yields and abuts against plane surfaces, preferably slightly striated for eliminating any freedom. When the speed of rotation has sufficiently lowered, the reaction of the resilient plate is the stronger, the contact of the plane surfaces is done away with, and the freedom towards increasing pitches is given to the rod on the balls.

It results therefrom that, when the propeller acts as a receiver, its speed of rotation considerably diminishing, the bearing takes place on the balls and the pivotingmovement in the direction of increasing pitches takes place by simultaneous inversions of the propelling stress and of the resistance to rotation. All the pivoting torques then tend to increase the pitch and the blades automatically pivot to a limit determined by an abutment. As soonas the engine is re-started at such an altitude that the aerodynamic torque overcomes the centrifugal torque, the blades resume their normal positions. By way of modification, it can be admitted that the resultant centrifugal torque slightly evercomes the aerodynamic torque, and the diflference is compensated by a spring. The difference of balance between both torques must remain sufficiently small in order that the spring may not prevent the blades from pivoting.

The invention moreover includes in its scope all the devices allowing to use the proposed mode of assemblage of the blades and the combination of the three fundamental torques for obtaining the automatic pivoting of the blades.

Figures 4 to 9 of the accompanying drawings illustrate, by way of example only, a form of construction of the propeller according to the invention, such as described and diagrammatically illustrated in Figs. 1 to 3.

In this example, the blades 1 and 1 are connected to the hub 2 in an identical manner; it will therefore be sufficient to explain how the blades 1 for instance are connected to the said hub.

The root of the blade 1* is provided with grooves, as shown at 3, these grooves fitting into corresponding notches of a socket 4, which is connected to the hub 2 by the torsion rod 5; the latter is secured to the socket 4, so as to rotate with the same, by means of a locking member 6. The rod 5 is secured, at its lower end, by means of flutes 7 fitting into corresponding flutes of a cap 8 secured'on the bottom 9 of the tube 10, rigid with the hub 2; one or more claws 11 prevent the rotation of the cap 8 relatively to the tube 10.

For resisting the radial stresses, the socket 4 is rendered rigid with a tube 11 co-axial with the rod 5 and tube 10, the tube 11 being radially supported by roller or ball bearings 12 and 13. An abutment 14 prevents the excessive lengthening of the rod 5 under the action of the centrifugal pull.

A counterweight 16 is pivoted, at 17, on the hub 2, and this counterweight is connected, by a link 18 pivoted, at 19 and at 20, on a collar 21 which is secured on the socket 4. The initial arrangement is such that the axis 22 of rotation of the propeller, the centre of gravity of the counterweight 16, and the pivoting axis 17 of this counterweight are normally in a straight line, so that the counterwei ht 16 is in unstable equilibrium under the action of the centrifugal stresses. As previously explained, as soon as the counterweight 16 abandons the position of unstable equilibrium, the centrifugal force which is exerted on the same tends to increase the pivoting movement of the blade.

A system of adjustment of the inclination of the blade 1 relatively to the socket '4, has been provided at 23, this adjustment being effected by means of the removable spanner 24. On the other hand, another adjustment can be effected by loosening the nut 25 securing the torsion rod 5,

this allowing to adjust the relative positions of the flutes 7 of this rod relatively to the corresponding flutes of the cap 8, by means of striae, more'particularly visible at 27. In this way, a slight loosening of the nut 25 suffices to release the washer 26 from the cap 8 and allowing the angular adjustment of the position of the rod 5, and, consequently, of the socket 4. The adjustment of the position of the counterweight 16 relatively to the socket 4, is obtained by previous loosening of the collar 21, and further tightening once the adjustment has been effected. I

In the foregoing, it has been seen that the automatic regulation of the pitch is obtained by balancing, at every instant, the following pivoting torques:

(1) An aerodynamic torque Ca due to the propelling stress and tending to reduce the pitch.

(2) An approximately constant centrifugal torque Kw proportional to the square of the speed a: of rotation and always tending to increase the pitch.

This torque is produced by the forward inclination of the pivoting axis accompanied by a suitable displacement of the neutral axis relatively to the axis of rotation in the direction of rotation. A centrifugal torque is thus generated which is greater than the natural centrifugal pivoting torque of the blade according to an amount Kw.

(3) An aerodynamic torque C's. due to the resistance to rotation of the blade and to the forward inclination of the pivoting axis. This torque C'a, proportional to the driving torque, tends to reduce the pitch by adding itself to Ca.

(4) A resilient reaction torque of the rod G0 proportional'to the pivoting movement, reckoned from a suitable origin.

(5) A variable centrifugal torque proportional to the pivoting movement and thus tending to return the blade, annulled by the action of a compensating counterweight always tending to increase the pivoting movement.

(6) A supplementary torque Kw due to the compensating device which represents the excess of the action of the compensating device on the variable centrifugal torque.

The equation for balancing the torques, by counting the pivoting movements positively towards the decreasing. pitches, is the following:

The adjustment of the compensating device modifies the coeflicient K, this allowing to con-. trol at will the sensitiveness.

A constant driving torque Ca is a linear function of the pivoting movement, so that CB+C'B=A+B0; therefore On the other hand, if V is the speed of the airplane, to is, for the blade, a linear function of 0, w=A' 0+3, so that normal speed is obtained by intersection of this latter straight line with the curve (2).

The normal speed is always stable as, for an increase of speed Am the pivoting movement A0 given by the curve of automaticity is smaller than that corresponding to the blade. In the direc tion of the decreasing pitches, if the sensitiveness is excessive, the blade moves toward its abutment without unstability.

The possibility of separating both sensitivenesses by displacement of the eccentric of the counterweight then constitutes an advantage; this being obtained by mounting the axis of the counterweight itself on a socket constituting an adjustable eccentric.

This type of propeller is particularly suitable for an engine provided with a compressor main-' taining the driving torque constant up to an altitions is nearly rigorously maintained when climbing, and when flying horizontally, the number of revolutions is very slightly decreased.

The invention includes in its scope all the combinations and even inversions of the pivoting torques by modification of the relative positions of the various members for satisfying all the requirements of applications different from that in which a compressor is used.

In fact, let us assume that this typeof propeller is used with an airplane capable of flying at very'high altitudes and provided-with an ordinary engine, the torque of which regularly de-- creases with the altitude about proportionally to atmospheric pressure. I

The propeller being adapted for a low altitude, at increasing altitudes the aerodynamic torques Ca and C'a very rapidly decrease when the altitude of flight increases. The pitch of the propeller would increase, in these conditions, much too quickly. The benefit obtained for climbing to a low altitude, would be acquired to the detriment of the flight at high altitude, for which At lower altitudes, the same number of revoluthe number of revolutions would diminish more rapidly than with an ordinary propeller.

In this case, it is necessary that the pivoting torque due to the tensile force should no longer bear on a centrifugal torque Kw but on the reaction C'a of the driving torque.

As, in these conditions, Ca and 0's. decrease, when climbing at increasing altitudes, nearly in the same way in function of the density of the. air, a favourable regulation of the pitch can be obtained at any altitudes.

For that purpose:

(1) The constant centrifugal torque giving the term Kw is eliminated or rendered very small by annulling the displacement of the neutral axis relatively to the axis of rotation, or by rendering it very small.

(2) The aerodynamic torque C'a, due to the reaction of the driving torque, is reversed by reversing the inclination of the pivoting axis which takes place rearwardly instead of forwardly.

(3) The blade is given an initial compensation to bending by angularly displacing it forwardly, about its pivoting axis, to theextent of a few degrees.

This displacement produces at the same time a centrifugal torque tending to increase the pitch and which compensates the natural centrifugal torsion torque of the blade.

Let us assume (Fig. 10) that the axis of rotation at A is perpendicular to the plane of the diagram, the pivoting axis being projected at A B and displaced relatively to O in reverse direction to the rotation w for an observer standing in front.

Let us first assume that the neutral axis extends in a plane perpendicular to the axis of ro tation it encounters since it is not displaced.

The resistance to rotation is T, proportional to the driving torque, at the distance Z from the point A where the neutral axis meets the pivoting axis.

Relatively to the point A, the moment of T is d =TZ perpendicular to the plane normal to the axis of rotation drawn through the neutral axis.

The pivoting rod is rearwardly inclined to the extent of a and the projection of on the pivoting axis is '=4 sin a=TZ sin a.

It is the pivoting torque C's. due to the reaction of the driving torque: it tends to increase the pitch.

The equation for the balance of the torques then assumes the form As, when climbing, the tense stress and the driving torque decrease with the density of the air approximately to the same extent, the difierence CaC'e, will remain null and the pitch will not vary.

It can be shown, and experience proves it, that, during all the period of climbing, the number of revolutions will remain constant, therefore equal to its maximum.

It will also remain, constant when flying horizontally, since it must have this same value at the maximum altitude and at the altitude for which the propeller has been devised. A uniform number of revolutions of the engine is thus obtained for all kinds of flight.

This allows to obtain a gain of at.least 20 to 30% over the time required for climbing, an increase of the maximum altitude to which the airplane can fly, and a gain over the speed when flying horizontally.

(2) If, at the beginning of a climb, C9. is greater than 0'8, a very slight decrease occurs in the number of revolutions from the ground to the maximum altitude the airplane can fly, and, for all horizontal flights, about exactly the same number of revolutions takes place as when climbing.

Figures 11 to 16 illustrate a form of construction of a propeller according to the invention, applicable to an engine provided with a com pressor.

This example presents the following characteristic features:

(1) The hub is constituted by a cylindrical sleeve 28 carrying, at its ends, two covers 29 and 30,one of which, on the rear side, is provided with teeth for the actuation. Bosses 31 receive the pivoting tubes 32.

(2) The parts, when assembled, form a single structure, the pivoting tubes 31 directly carrying the blades 33 which are provided with large screw-threads 34.

(3) The abutting of the guide tube limiting the lengthenings of the rod 35 takes place above the axis of rotation, through a ring 36 composed of two parts held by a socket 37.

(4) The guide tube 32 carries, at its upper part, two rows of small rollers 38 so arranged that the side stress is equally divided between both rows of rollers.

(5) The torsion rod 35 is held at both ends by identical screw-threads 39.

(6) The abutting in both directions directly takes place on the counterweights 40 through an abutment plate 41. v

(7) Besides the overloading of the counterweights, various adjustments are provided:

(a) Displacement of the counterweight The counterweight isclamped on a cross member 42 provided on both faces with a different number of teeth 43. Thus, by advancing to the extent of one tooth on one side, and by moving back to the extent of one tooth on the other side,

an accurate micrometric adjustment is obtained.

(b) Displacement of the eccentric The socket 44 of the counterweight is eccentrically arranged in its housing. By causing it to turn, the eccentric is displaced and it is possible to separate the sensitivenesses for the increasing pitches on the one hand, and for the decreasing pitches, on the other hand.

The socket is stopped by means of teeth 45 provided on a finger 46.

Finally, for all the types of propeller, use is made of rods 35 having a greater torsional resiliency than a solid cylindrical rod which, for a given surface, ensures the maximum rigidity to torsion.

With a solid rod, for a given pivoting movement the rate of torsional stress is proportional to the radius, whilst the rate of the centrifugal elongation stress is in reverse ratio to the square v.of the radius.

There is therefore a radius ensuring the minimum stress and which cannot be departed from.

In order to have wider limits of adaptation, it is necessary to divide the section of the tube into elements of rectangular, triangular or like shape, ensuring a much greater torsional resiliency.

A central core may be kept and the remaining section of the rod can be cut out in the form of small blades or wings (Fig. 14).

The core can be dispensed with, or the section of the tube can be cut out in any other manner so as to divide it into elements much more distortable by torsion than the solid circular section (Figs. 15 and 16).

It is also possible, by increasing the torsional resiliency, to give to the rod a greater section allowing it to operate at anarbitrarily chosen rate. The rod will thus be mounted as illustrated in Fig. 13. Moreover, owing to the greater resiliency, the length of the rod can be diminished and, consequently, the weight of the whole.

What I claim as my invention and desire to secure by Letters Patent is:-

1. In a propeller having a variable pitch, a hub, blades, means for pivoting each blade on the hub about an oblique geometrical axis with respect to the geometrical axis of the hub, the blades being arranged so that the geometrical extension of their neutral axispasses outside the geometrical axis of the hub and so that in a predetermined initial position this neutral axis is in a-plane perpendicular to the geometrical axis of the hub, and resilient means for bringing back the blades to this initial position.

2. In a propeller having a variable pitch, a hub, blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, means comprising counterweights in unstable equilibrium with respect to the centrifugal force in the initial position for assisting the pivoting of the blades when this pivoting has commenced.

3. In a propeller having a variable pitch, a hub, blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect tothe geometrical axis of the hub, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, resilient means for bringing back the blades to a predetermined initial position, means comprising counterweights in unstable equilibrium with respect to the centrifugal force in the said initial position for assisting the pivoting of the blades when this pivoting has commenced.

to the geometrical axis of the hub and not meeting same, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub and so that in a predetermined initial position this neutral axis is in a plane perpendicular to the geometrical axis of the hub, and resilient means for bringing back the blades to this initial position.

6. In a propeller having a variable pitch, a hub, blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub and not meeting same, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, means comprising counterweights in unstable equilibrium with respect to the centrifugal force in the initial position for assisting the pivoting of the blades when this pivoting has commenced.

7. In a propeller having a variable pitch, a hub, blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub and not meeting same, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, resilient means for bringing back the blades to a predetermined initial position, means comprising counterweights in unstable equilibrium with respect to the centrifugal force in the said initial position for assisting the pivoting of the blades when the pivoting has commenced.

8. In a propeller having a variable pitch, a hub,

blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub, a rod of tension and torsion arranged according to the geometrical pivoting axis, means for securing one end of this rod to the hub and means for securing the other end of this rod to the blade.

9. In a propeller having a variable pitch, a hub. blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub, the blades being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, a rod of tension and torsion arranged according to the geometrical pivoting axis, means for securing one end of this rod to the hub, means for securing the other end of this rod to the blade.

10. In a propeller having a variable pitch, a

hub, blades, means for pivoting each blade on the hub around an oblique geometrical axis with respect to the geometrical axis of the hub, the blades-being arranged so that the geometrical extension of their neutral axis passes outside the geometrical axis of the hub, a rod of tension and torsion arranged according to the geometrical pivoting axis, means for securing one end of this rod to the hub, means for securing the 'other end of this rod to the blade, means com- 

